Fighting Fungus – Know Your Enemy

by April K. Sievert, GBL Director

Hot and rainy summers are certainly hard on the climate within our repository! In order to preserve the artifacts collected 80 years ago by Glenn A. Black at the Angel Mounds site, we need to contend with environmentally-related dangers to both staff and stuff. One of these is mold, tiny fungal bodies and spores that feed off organic materials. Molds love to grow where its dark and moist, and the inside of a box of archaeological bone may be ideal places under rising heat and humidity. Normally, as GBL Director, I don’t get the chance to get down and dirty, so I was happy to be able to arm myself with protective gear and start to figure out what we are dealing with .

April Sievert starting some mold research

We discovered serious mold problems at around the same time that we received news that we were awarded funding for Curating Angel Mounds, through the Save America’s Treasures program of the National Park Service, administered by the Institute for Museum and Library Services (IMLS). The first task was to have an air quality test done. Results of this test, which is facilitated by IU’s Environmental Health and Safety Department, shows higher levels of a common mold family—Aspergillus/Penicillium— in the air in our Angel Mounds Repository. The report indicates mold likely originating from within the room itself. This mold was likely being generated by moldy materials, most likely the acidic brown paper bags used for artifacts, some of which show both water damage and signs of mold (molds love acidic materials).

Test results on mold identified in the air the Angel Curation room

Mold produces spores from tiny branching filaments called hyphae. The mold can be inactive (dried spores that look like dust and can remain dormant for years) or active, meaning that the hyphae are happily making new spores. The hyphae are like tiny straws that suck water out of the substrate (whatever the mold is growing on) so that they can grow and make more spores. Active mold presents as smeary, fluffy, or hairy patches on surfaces. Molds grow well at temperatures between 60-90° F and RH above 65%. We deployed a large noisy air scrubber to remove the spores from the air, and extra dehumidifiers to bring the humidity down.

There are two quite different kinds of mold on the bags and artifacts from Angel Mounds that are visible with the naked eye. One presents as a white deposit adhering to a scratch on the bone surface.

White deposits in crevice on faunal bone

The network of hyphae and spores become visible under high-power magnification using the polarizing filter on our metallurgical microscope. White deposits on at 500x magnification show a blurry mass of filaments the represent actively growing mold.

White mold hyphae

The white mold is consistent with the Aspergillus/Penicillium group and appears to like cuts or crevices in the bone cortex. Softer spongier bone provides easily accessible nutrients for the fungus. A very different brown mold that flourishes on a small proportion of bags shows up as fuzzy dots.

Bag fragment from 1939 showing brown active mold

Bones within these bags sport dense patches of hyphae with dark brown spores. After initial cleaning, the location still had a tenacious colony of brown spores.

Brown mold with well-developed fruiting bodies and spores (500x magnification)
Mold colony after one cleaning with alcohol (500x magnification)

The clearly-seen spores are about 10 microns long and 6 microns wide, appear iridescent under polarized light, and are quite lovely. We’ll be sending samples of these beauties to a lab for more precise identification. So, stay tuned for more on mold, and the conservation treatment we are using!

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